OMEGA EP: High-Energy Petawatt Capability for the OMEGA Laser Facility

Transcription

1 OMEGA EP: High-Energy Petawatt Capability for the OMEGA Laser Facility Complete in 2007 J. Kelly, et al. University of Rochester Laboratory for Laser Energetics Inertial Fusion Sciences and Applications Biarritz, France 4 9 September 2005

2 Collaborators L. J.Waxer, V. Bagnoud, I. A. Begishev, J. Bromage, B. E. Kruschwitz, T. J. Kessler, J. A. Zuegel, S. J. Loucks, D. N. Maywar, R. L. McCrory, D. D. Meyerhofer, S. F. B. Morse, J. B. Oliver, A. L. Rigatti, A. W. Schmid, C. Stoeckl, S. Dalton, L. Folnsbee, M. J. Guardalben, R. Jungquist, J. Puth, M. Shoup, and D. Weiner University of Rochester Laboratory for Laser Energetics

3 Summary Two 2.6-kJ petawatt beamlines will be integrated into OMEGA: OMEGA Extended Performance (EP) OMEGA EP is under construction and will be completed in The laser is located in a new building adjacent to the existing OMEGA facility to allow integrated experiments. It has a variety of configurations with up to four 10-ns, 6.5-kJ UV beams to a separate target chamber, two of which can be used in short-pulse (SP) mode SP beam 1: up to 2.6 kj and 10 ps and longer or 1 kj at 1 ps SP beam 2: up to 2.6 kj at 80 ps and longer OMEGA/OMEGA EP will provide a flexible HED facility, significantly extending LLE s research capabilities. G6668

4 OMEGA EP s five primary missions complement and extend LLE s current research activities 1. Extend direct-drive ICF research capabilities high-energy and highbrightness backlighting 2. Perform fast-ignition (FI) concept research integrated experiments 3. Develop advanced backlighter techniques for HED physics 60-beam OMEGA OMEGA EP 4. Conduct ultrahigh intensity laser matter interaction research 5. HED physics combination of long/short pulse beams in the OMEGA EP chamber E11888f

5 Short-pulse OMEGA EP beams can be directed either to OMEGA or new EP target chamber OMEGA target chamber OMEGA EP target chamber OMEGA Laser Bay Compression chamber Beam 1 2 Main amplifiers Short pulse Short pulse (IR) IR energy on target (kj) Intensity (W/cm 2 ) Focusing (diam) G5546w Beam 1 1 to 100 ps 2.6 kj, ps grating limited* <10 ps > 80% in 20 μm Beam 2 1 to 100 ps 2.6 kj, ps beam combiner limited <80 ps ~ > 80% in 40 μm *Grating damage threshold is 2.7 J/cm 2 (beam normal). OMEGA EP Laser Bay Booster amplifiers R. L. McCrory talk J. D. Zuegel poster J. Bromage poster B. E. Kruschwitz poster

6 The OMEGA EP long-pulse UV energy is a function of pulse width with a potential of 6.5 kj per beam at 10 ns Frequency conversion uses an 11 mm/9 mm type I/II KDP/KD*P setup with mirror transport (similar to OMEGA) to the OMEGA EP target chamber Conversion crystals separate from the target chamber. decouples on-target pointing from crystal tuning no unconverted light in the chamber The long-pulse performance limiting optic is the first UV mirror. baseline damage fluence of 5.2t 1/3 (t is the Gaussian pulse width in ns) potentially improving to 7.0t 1/3 Per beam Square pulse width (ns) Potential UV on target (kj) Potential intensity (1-mm spot) (W/cm 2 ) G6669 With 4 beam long-pulse operation greater than 25-kJ UV total in 10 ns is available.

7 The OMEGA EP short-pulse capability presented technical challenges in a number of areas Fast off-axis parabola on-target pointing and focusing Broadband high-repetition-rate front end (not shown) NIF architecture folded to fit single beam target retro-isolation Pulse compression high-damage-fluence gratings grating tiling grating wavefront correction tiling gap apodization G6670 These technical challenges have been met.

8 The OMEGA EP short-pulse capability presented technical challenges in a number of areas Fast off-axis parabola on-target pointing and focusing Broadband high-repetition-rate front end (not shown) NIF architecture folded to fit single beam target retro-isolation Pulse compression high-damage-fluence gratings grating tiling grating wavefront correction tiling gap apodization G6670a NIF technology development has been significantly leveraged.

9 OMEGA EP uses a broadband high-repetiton-rate, high-energy front end A high repetition rate (5 Hz) at high energy (500 mj) is required to set up the pulse shape. Short-pulse oscillator 200 fs at 76 MHz Stretcher 300 ps/nm Two-stage OPCPA 2w To beamline Glass amplifier Large-aperture ring amplifier, 5Hz G6671 Pulse shaping

10 Excellent OPCPA system ouput energy and stability performance is achieved Seed 600 pj, 300 ps/nm Pump 300 mj, 2.4 ns LBO preamplifier mm 1.4 J, 2.4 ns 63 mj LBO power amplifier 11 mm 530 mj, 5 Hz The saturated preamplifier produces much of the gain The unsaturated power amplifier achieves 35% pump-to-signal conversion efficiency At full energy, the energy stability is typically ~1% rms (over 100 shots) Signal energy (mj) Power amplifier energy 530 mj Pump energy (mj) E13798a V. Bagnoud et al., Opt. Lett. 30, 1843 (2005).

11 Development of a pump laser with high spatial and temporal fidelity was key to OPCPA success* 300 Hz Vacuum spatial filter FF CCD Singlelongitudinalmode oscillator Temporal pulse shaping Regenerative amplifier Nd:YLF λ/2 Image plane Apodizer TFP Nd:YLF Q-switch and cavity dump PC λ/2 SHG NF CCD E13794b Magnetorheological finishing (MRF) significantly improves rod optical quality. Before MRF 20-mm aperture *V. Bagnoud et al., Applied Optics 44, 282 (2005). After MRF mm Pump fluence at 2ω, the laser produces 0.86 J when using a 10-mm-square apodizer % rms mm Temporal pulse shape 2.5-ns, 20th order super-gaussian Normalized power Measurement Fit Nanoseconds

12 OMEGA EP adapts NIF technology to a single-beam folded architecture From Pointing/centering laser sources Up-collimator mirrors Fold mirror Booster amplifier PEPC Vacuum window POL2 Injection lens 38 m Transport spatial filter Diagnostic beam splitter To compressor Deformable mirror Cavity end mirror POL1 Rejected light 23 m Cavity spatial filter Main amplifier G5221g LLE unique

13 The amplifiers use NIF disks in an LLE-engineered, water-cooled-flash-lamp, single-segment amplifier Designed for LLE-style handling equipment to reduce maintenance cost Water-cooled lamps for improved (<2 h) repetition rate with same gain as the NIF Reduced-voltage (15-kV) for compatibility with existing OMEGA power conditioning OMEGA lamp assemblies OMEGA EP lamp assembly G5565a

14 High PEPC contrast is required to protect the injection mirror from a target back-reflection Calc assumes pol. Tp/Ts = 0.98/0.005 Injection mirror damage 1w, target back-reflection risk Amplifiers are not saturated in short-pulse operation PEPC must provide backreflection isolation Contrast > 500:1 everywhere in the aperture for 2 kj target retro G6672

15 LLE has developed a high-contrast plasma electrode Pockels cell (PEPC) for OMEGA EP** OMEGA EP requires a switching contrast >500:1 over entire aperture for protection from retroflections. LLE has adapted LLNL-developed PEPC technology.* circular windows for reduced stress birefringence larger-area plasma channel for reduced pinching Plasmas Cathodes Cross section Anodes KDP crystal in glass midplane Windows E-field 40 cm Vacuum plenum/baffle E13805 *M. A. Rhodes et al, Appl. Opt (1995). **Mark Rhodes, Phil Arnold, & Doug Larson, LLNL

16 The measured PEPC active contrast is >500:1 everywhere in the aperture G6673 V sw = 0 V sw = 18.1 kv Active switching contrast Min. contrast = 1,000:1 (Two measurements shown with cell translated to move shadow of secondary mirror. Each measurement averaged 20 dark images.)

17 Four-pass operation requires double pulsing of the PEPC using inductive adder driver technology TCC (1150 ns) ns/20 kv 100-ns rise/fall into 12.5 ohms Ω ouput, 4 parallel 50=Ω lines Inductive adder technology utilizes a series transformer connection of simultaneously triggered, ground-referenced MOSFET driver modules. Designed and assembled by E. G. Cook of LLNL for LLE (picture of LLNL unit). G6674 Transformer core Paralleled MOSFET driver module 1 of 30

18 A four-grating vacuum compressor configuration meets the beam size restriction of the OMEGA target chamber port 5.5 m 4.2 m 23 m To diagnostics or to OMEGA EP chamber To OMEGA chamber Input beams Beam combiner 1740 lines/mm, cm, high damage fluence MLD tiled grating assemblies Deformable mirrors G5601g

19 MLD grating samples are now meeting OMEGA EP s 2600 J at 10 ps requirement Recently, samples from various vendors, including LLE have consistently met OMEGA EP s damage-threshold specification. 4 Jul 03 Sep 04 Fluence (J/cm 2 ) J OMEGA EP requirement at 61 incidence (G4) L1 L2 #13 #14 #16 Non-LLE stack All fluences are beam fluences, N-on-1 values. All tests are at 61 incidence, s-polarization, 10 ps pulse. Sample 1 Sample 2 Sample G6313d

20 LLE has damage tested MLD gratings over the entire OMEGA EP pulse-width range Meets damage threshold for petawatt power Exceeds 2.6 kj at 10 ps damage threshold Damage fluence t 0.46, t = pulse width in ps G6676

21 The OMEGA EP tiled-grating assemblies features flexure support of outboard tiles and 5-nm tile positioning resolution 1.41 m 43 cm E13795a 3 degrees of freedom (DoF) per outboard tile controlled using electrostrictive actuators and capacitive sensors Tiling alignment DoF (6 total) independent of compressor alignment DoF (3 total) 320-kg (700-lb) total weight of assembly

22 Tile-to-tile alignment is established interferometrically and maintained using capacitive sensors and closedloop position control G6677

23 LLE has demonstrated closed-loop control of tiled gratings to produce an assembled focal spot Before After Alignment error (waves) Tilt Tip Piston Loop iterations Normalized signal 1 0 x y x y Diffraction limit Diffraction limit E13554

24 Tiling gaps introduce spatial modulation that may threaten downstream optics* TG2 TG3 Relative intensity Input X (m) TG1 TG4 TG X (m) OAP X (m) G6678 Modulation from gaps in TG1 threatens TG4 Modulation from all of the TG s threatens downstream optics, especially the off-axis parabola *T. Zhang et al., Opt. Commun. 145, 367 (1998).

25 Simple apodization may offer the best solution to grating-gap modulation TG2 TG3 TG1 TG4 Relative intensity Input X (m) TG X (m) OAP X (m) ~50% shadowing yields a reasonable trade-off between modulation and energy loss 7.5% energy penalty Transition width is compatible with system pinholes G6679

26 A deformable mirror after the compressor corrects tiled-grating wavefront errors Wavefront Far-field intensity Grating aberration μ Strehl = 0.17 μ Residual wavefront after correction G6680 μ Strehl = 0.81 μ

27 A comprehensive suite of diagnostics is planned to characterize the on-target pulse intensity Pulse-width measurement in the range <1 ps to 100 ps using a combination of streak cameras (~8 100 ps) and EO-SPIDER ( ps) Near-field intensity and phase measurements, along with transport optic characterization are used to calculate the focal spot. E13688 J. Bromage poster

28 The laser beam from OMEGA EP will be focused with a 23 f/2 off-axis parabola inside the target chamber A fast-focusing optic is necessary to meet the 20-μm-diam focalspot requirement. The size of the target chamber port limits the input beam size. The beam path has to stay clear of the cryogenic target handling equipment. Target Parabola Cryo equipment E13316a

29 The OMEGA EP building was completed in February 2005 April 2004 January 2005 OMEGA Target Bay Mechanical room Laser bay Laser bay slab, 1 m Capacitor bay OMEGA EP Laser Bay The source laser was installed in April E13574c

30 An OMEGA EP Use Plan is under development The OMEGA EP Use Plan will define the expected operating parameters and availability, the avenues for non-lle users to obtain access, and initial experimental campaigns. The Use Plan will be completed in Spring An informational and informal discussion meeting will be held at the 2005 APS/DPP meeting. A workshop will be held at UR/LLE in January to allow potential users to propose experiments and discuss access availability and - to consider capabilities required to carry out the experiments. If you wish to be informed of, or participate, in this planning activity and be included in the mailing list, contact E13897 David D. Meyerhofer Laboratory for Laser Energetics ddm@lle.rochester.edu

31 Summary/Conclusions Two 2.6-kJ petawatt beamlines will be integrated into OMEGA: OMEGA Extended Performance (EP) OMEGA EP is under construction and will be completed in The laser is located in a new building adjacent to the existing OMEGA facility to allow integrated experiments. It has a variety of configurations with up to four 10-ns, 6.5-kJ UV beams to a separate target chamber, two of which can be used in short-pulse (SP) mode SP beam 1: up to 2.6 kj and 10 ps and longer or 1 kj at 1 ps SP beam 2: up to 2.6 kj at 80 ps and longer OMEGA/OMEGA EP will provide a flexible HED facility, significantly extending LLE s research capabilities. G6668

32 Smoothing by a spatial chirp can mitigate fluence modulation TG2 TG3 TG1 TG4 TG1-TG2 slant distance is shortened and the TG3-TG4 slant distance is lengthened by equal amounts ~15 cm Overall compression ratio is unchanged Output beam aquires a spatial chirp and the beam size in the horizontal direction grows slightly (~2 mm at 1% level) E12351c

33 The first OMEGA EP deformable mirror (DM) has achieved closed-loop control Wavefront map WFS spot pattern Open loop Closed loop WFS Actual DM G6100c Interferogram Interferometer DM

34 OMEGA EP can deliver four long-pulse UV beams with up to 6.5 kj each to the OMEGA EP target chamber E13932a The four long-pulse (1 to 10 ns), UV beams are focused with a f/8.5 lens and come in at 23 to the target normal. The long-pulse beams can be operated independent of the 60-beam OMEGA system for high-energy-density physics experiments. OMEGA EP can also be configured as two or three f/8.5 long-pulse UV beams with one or two f/2 short-pulse, IR beams on-target for short-pulse experiments that require a preformed plasma.

35 A refractive/diffractive lens results in 38% reduction in OPD and a 32% smaller focal spot Injection focus lens with DOE surface Fused silica, plano/convex Fused silica, with DOE Y fan 2 OPD at final focal plane 2 X fan ±1.1 l G